1. Field of the Invention
This invention relates to a method for stabilizing organic substrate materials to light, and more particularly to a method for stabilizing organic compounds, especially organic dyes and photographic dye images to light.
2. Brief Description of the Prior Art
In general, it is accepted that organic substances, for example, such as organic dyes tend to fade by the action of light. Extensive investigations have been carried out in various technical fields including those for printing ink, textile dyeing as well as color photography, attempting to enhance light fastness of organic dyes.
The present invention is advantageously applied to the improvement of the light fastness of these organic substrate materials.
In the following description, the term "organic substrate material" or "organic substrate" refers to materials appearing colored or colorless to human vision under the illumination of sunlight, including not only those with the absorption maximum in the visible region of spectrum, but also those the absorption maximum of which lies in the ultraviolet region as in the case of optical whitening agent or in the infrared. Phrased differently, the organic substrate materials of the present invention include those having their absorption maxima at the wavelength of from 300 to 800 nm. These organic substrate materials occur particularly in photographic materials, e.g., color films, prints, diffusion transfer units, etc., in colored polymers useful as agricultural vinyl cover sheets, umbrellas, tents, etc.; fluorescent whitening agents; and dyed textiles, etc., and this invention is directed to improving the light fastness of these materials in each of these environments.
In the present specification, the term "dye" or "dyestuff" refers to organic materials which appear colored to the human eye under the illumination of sunlight.
In the present specification, the term "light" conceptually involves electromagnetic radiation with wavelengths up to about 800 nm, thus including ultraviolet ray below 400 nm, visible light of from about 400 nm to about 700 nm and infrared or from about 700 nm to about 800 nm.
It is already widely known that organic substrate materials such as dyes or dyestuffs tend to fade under the influence of light irradiation; and a number of technical reports dealing with the methods of suppressing such a tendency or of improvement of the light fastness of such materials are known. For example, U.S. Pat. No. 3,432,300 discloses that the light fastness of organic compounds such as indophenol, indaniline, azo and azomethine dyes against visible and UV light is improved by the use of certain phenol derivatives containing a fused heterocyclic structure. As is described in, C. E. K. Mees and T. H. James, The Theory of the Photographic Process, Chapter 17, published by Macmillan Inc., (1967), silver halide color photographic products generally give rise to azomethine or indaniline dyes formed by the reaction of the oxidation product from an aromatic primary amine developing agent with a coupler. A number of techniques are known with respect to methods for improving the stability of images obtained from these dyes, that is, colored images, to light; for example, there are known hydroquinone derivatives as described in U.S. Pat. Nos. 2,360,290, 2,418,613, 2,675,314, 2,701,197, 2,704,713, 2,728,659, 2,732,300, 2,735,765, 2,710,801, and 2,816,028, British Pat. No. 1,363,921, etc.; gallic acid derivatives as described in U.S. Pat. Nos. 3,457,079 and 3,069,262, Japanese Patent Publication 13496/1968, etc.; p-alkoxyphenol derivatives as described in U.S. Pat. Nos. 2,735,765 and 3,698,909; chroman or coumarane derivatives as described in U.S. Pat. Nos. 3,432,300, 3,573,050, 3,574,627, 3,764,337, 3,574,626, 3,698,909 and 4,015,990 and the like. These compounds are effective to prevent the fading or discoloration of dye images induced by light to a certain extent, but not to a satisfactory extent.
British Pat. No. 1,451,000 discloses that the stability to light of organic substrate materials is enhanced by the use of azomethine quenching compounds which have their absorption-maximum at a longer wavelength than the substrate material; however, unfortunately the fact that the azomethine quenching compound is colored itself adversely affects the color hue of the substrate material.
Further, metal chelates can be used for the prevention of degradation of polymeric substances caused by the action of light as is described in J. P. Guillory and R. S. Becker, J. Polym. Sci. Ed., 12, 993 (1974), and R. P. R. Ranaweera & G. Scott, J. Polym. Sci., Polym. Let. Ed., 13, 71(1975), etc. Stabilization of dyes against light by the use of metal chelates is also described in Japanese Patent Application (OPI) 87649/1975 and Research Disclosure, 15162(1976). However, the disclosed metal chelates exhibit an unsatisfactory light fastness together with an undesirably poor solubility in common organic solvents. The latter imposes a limitation on the working concentration of such a chelates in the system in concern, thus leading to an insufficient function of light fastness. Moreover, these chelates cannot be present in a high concentration since they themselves are comparatively deeply colored, adversely affecting the color hue and color purity of the dyes to be protected.
In addition to the foregoing, agents suitable for improving the light fastness of cyan dyes and particularly cyan dye images have not been known.